1. Field of the Invention
The present invention relates to a battery charger for charging secondary batteries, such as nickel-cadmium batteries and nickel-hydrogen batteries.
2. Description of the Related Art
Chargeable batteries are normally used for powering portable devices. In an operation that can be repeated multiple times, the chargeable batteries are removed from the portable device, charged with a battery charger, and subsequently reloaded into the portable device. Users of these portable devices have expressed a desire to know the amount of charge a battery has at the beginning of use, since a sudden loss of battery power during use degrades operating efficiency. These users have also indicated a desire to know, when charging the batteries, how much time will be required to complete the charging operation.
In order to meet these demands, batteries with charge amount displays have been proposed in recent years, such as that disclosed in Japanese Patent Application Publication No. 2001-116812. In this proposal, a microcomputer is built into the body of the battery for accumulating load current and operating time. The charge amount of the battery (remaining capacity) is displayed on an LED or the like by comparing the accumulated quantities to the rated capacity of the battery. Further, a battery charger such as that disclosed in Japanese Patent Application Publication No. 10-174308 proposes displaying the charge amount of the battery (remaining capacity) with a plurality of LEDs provided in the battery charger.
However, in the former example of the battery with charge amount display, it is necessary to equip the battery itself with a microcomputer or other means to accumulate the load current and operating time. Moreover, the user demands mentioned above cannot be met with batteries not equipped with such microcomputers. In the latter example of the battery charger, while it is possible to display the charge amount (remaining capacity) of a battery, the battery charger must be equipped with a plurality of LEDs, which is disadvantageous both spatially and economically.